Browsing by Subject "Ecdysone"
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Item Open Access A Genetic Mosaic Screen Reveals Ecdysone-Responsive Genes Regulating Drosophila Oogenesis.(G3 (Bethesda, Md.), 2016-08) Ables, Elizabeth T; Hwang, Grace H; Finger, Danielle S; Hinnant, Taylor D; Drummond-Barbosa, DanielaMultiple aspects of Drosophila oogenesis, including germline stem cell activity, germ cell differentiation, and follicle survival, are regulated by the steroid hormone ecdysone. While the transcriptional targets of ecdysone signaling during development have been studied extensively, targets in the ovary remain largely unknown. Early studies of salivary gland polytene chromosomes led to a model in which ecdysone stimulates a hierarchical transcriptional cascade, wherein a core group of ecdysone-sensitive transcription factors induce tissue-specific responses by activating secondary branches of transcriptional targets. More recently, genome-wide approaches have identified hundreds of putative ecdysone-responsive targets. Determining whether these putative targets represent bona fide targets in vivo, however, requires that they be tested via traditional mutant analysis in a cell-type specific fashion. To investigate the molecular mechanisms whereby ecdysone signaling regulates oogenesis, we used genetic mosaic analysis to screen putative ecdysone-responsive genes for novel roles in the control of the earliest steps of oogenesis. We identified a cohort of genes required for stem cell maintenance, stem and progenitor cell proliferation, and follicle encapsulation, growth, and survival. These genes encode transcription factors, chromatin modulators, and factors required for RNA transport, stability, and ribosome biogenesis, suggesting that ecdysone might control a wide range of molecular processes during oogenesis. Our results suggest that, although ecdysone target genes are known to have cell type-specific roles, many ecdysone response genes that control larval or pupal cell types at developmental transitions are used reiteratively in the adult ovary. These results provide novel insights into the molecular mechanisms by which ecdysone signaling controls oogenesis, laying new ground for future studies.Item Open Access The Regulation of Body and Wing Disk Growth in Manduca Sexta(2009) Tobler, AlexandraA key question in developmental biology is how organisms attain a final size. Deviations in growth patterns can produce different/new phenotypes and these changes can play fundamental roles in ecology and evolution. The size of an organism and of its constitutive organs is determined by the growth rate and the duration of the growing period. In insects, peptide hormones such as insulin-like growth factors have been shown to be involved in determining the growth rates by coordinating metabolism, cell proliferation and cell size. In contrast, steroid hormones, such as ecdysone, are involved in determining life stage transitions, and thus the termination of the growing period. Although it is clear that insulin and steroid hormones are both involved in the regulation of growth, the ways in which these two regulators interact is yet to be determined. Furthermore, it is not clear how organs and body growth are coordinated during development to arrive to their correct proportions. In this study, using the tobacco hornworm Manduca sexta and its wings as a model system, I examine the developmental mechanisms involved in the regulation of organ growth and how developmental processes can drive morphological evolution. First, I examine how the hormonal events that take place during the termination of the body growth period affect wing disk growth. Second, by using gene expression assays and in vitro cultures, I examine the interaction between bombyxin, the Lepidopteran insulin-like growth factor, and ecdysone, the molting hormone, and their contributions to wing imaginal disk growth. Finally, by using three different size strains of M. sexta, I examine the developmental basis of the allometric relationship between the wings and the body. My results show that during the final instar of M. sexta larval development, wing imaginal disks are sensitive to the hormonal events that terminate the growth period. Furthermore, I show that the bombyxin requirement for wing disk growth is restricted to the early days of the final instar unlike the constitutive effects seen in other species. After the larva has passed a particular critical weight, bombyxin is not necessary for wing disk growth, although its absence does decrease the growth rate. In contrast, ecdysone is required for promoting the growth of wing imaginal disks primarily through its stimulation of cell proliferation. Finally, I show how selection on body size has unpredictable consequence for the response of wing size. These results demonstrate how specific allometries have a developmental basis in the cross-talk of the various signals that regulate growth itself. Therefore, direct selection on allometric relationships may not need to be strong in order to hold scaling relationships constant, at least over short evolutionary periods.